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Britain's Chris Froome crosses the finish line of the seventeenth stage of the Tour de France cycling race over 65 kilometers (40.4 miles) with start in Bagneres-de-Luchon and finish in Saint-Lary-Soulan, Col du Portet pass, France, Wednesday July 25, 2018. The Tour de France thinks it has some solutions to liven up the action with today's shorter mountain stage with three grueling climbs, including an uphill finish, intermediate bonus sprints, and a Formula One-like grid start. (AP Photo/Peter Dejong)

Up amid the thin and misty air of the Col du Portet — rated the second toughest climb in Tour history — Froome cracked on the feared 17th stage through the Pyrenees on Wednesday, solidifying Sky teammate Geraint Thomas's hold on the yellow jersey.

"Froomey said on the radio @ maybe 5K or 4K to go that he wasn't feeling super," Thomas said after increasing his lead to nearly two minutes over Tom Dumoulin. "That gave me confidence because I knew if Froomey suffered, everyone suffered.

"I didn't want him to have a bad day like he did but it just gave me confidence knowing someone of Froomey's stature was struggling, and I just knew I would be able to respond to the attacks."

The British rider's day then went from bad to worse as he crashed when police mistook him for a fan on the way down the mountain, with his bodyguard also on a bike.

Froome had put a black raincoat over his racing uniform to keep warm and when police ordered him to stop, he lost control.

Team Sky said the rider was not injured in the incident, which came a day after police used tear gas to disperse a farmers' protest that had blocked the road with bales of hay.

Froome was among a large group of riders whose eyes needed treatment due to the tear gas.

He has been a repeated target of fans after he was cleared of doping five days before the race began. The four-time champion had been racing under the cloud of a potential ban for using twice the permitted level of salbutamol during his victory at the Spanish Vuelta in September.

Froome said he has been repeatedly spat at since the race started, and that spectators have punched him and tried to make him fall off his bike.

He is attempting to match the Tour record of five victories shared by Jacques Anquetil, Eddy Merckx, Bernard Hinault and Miguel Indurain, but appeared to concede defeat.

"We've just got to look after (Thomas) now," Froome said. "I've won the last three Grand Tours and G has ridden an absolutely faultless race this year, so he fully deserves to be in the yellow jersey, and fingers crossed he finishes it off and gets the job done in Paris."

The stage was a strong signal that Froome has reached his limit after winning the Tour and Vuelta last year, and the Giro d'Italia in May.

"What you've got with Chris is he'll empty the tank," Team Sky principal Dave Brailsford said. "He deserves a lot of credit having gone to the Giro ... He's a great, great champion. He's not out of it necessarily ... If anybody can bounce back it's Chris Froome — I wouldn't rule him out."

After a less arduous Stage 18 on Thursday, there is another mountainous leg in the Pyrenees on Friday. There's an individual time trial on Saturday before the three-week race ends Sunday in Paris.